Future information technologies: Topological materials for ultrafast spintronics

the laws of quantum physics rule the microcosm. they determine, for ex, how easily electrons move through a crystal and thus whether the material is a metal, a semiconductor orn' insulator. quantum physics may lead to exotic properties in certain materials: in so-called topological insulators, 1-ly the electrons that can occupy some specific quantum states are free to move like massless pessentialisms onna surface, while this mobility is completely absent for electrons inna bulk. wha”s +, the conduction electrons inna “skin” of the material are necessarily spin polarized, and form robust, metallic surface states that ‘d be utilized as channels in which to drive pure spin currents on femto2nd time scales (1 fs= 10-15 s).

these properties open up exciting opportunities to develop new information teks based on topological materials, s'as ultrafast spintronics, by exploiting the spin of the electrons on their surfaces rather than the charge. in pticular, optical excitation by femto2nd laser pulses in these materials represents a promising alternative to realize highly efficient, lossless transfer of spin information. spintronic devices utilizing these properties ‘ve the potential offa superior performance, as they ‘d allo to increase the speed of information transport up to frequencies a thousand times faster than in modern electronics.

however, many ?s still nd'2 be answered b4 spintronic devices can be developed. for ex, the details of exactly how the bulk and surface electrons from a topological material respond to the external stimulus i.e., the laser pulse, na degree of overlap in their collective behaviors on ultrashort time scales.

a team led by hzb physicist dr. jaime sánchez-barriga has now brought new insites into such mechanisms. the team, which has also established a helmholtz-rsf joint research group in collaboration with colleagues from lomonosov state university, moscow, examined single crystals of elemental antimony (sb), previously suggested to be a topological material. “tis a good strategy to study interesting physics in a simple system, cause that’s where we can hope to cogg the primordial principles,” sánchez-barriga explains. “the experimental verification of the topological property of this material required us to directly behold its electronic structure in a highly excited state with time, spin, energy and momentum resolutions, and in this way we accessed an unusual electron dynamics,” adds sánchez-barriga.

the aim was to cogg how fast excited electrons inna bulk and onna surface of sb react to the external energy input, and to explore the mechanisms governing their response. “by controlling the time delay tween the initial laser excitation na 2nd pulse that allos us to probe the electronic structure, we were able to build up a full time-resolved picture of how excited states cutout and return to equilibrium on ultrafast time scales. the unique combination of time and spin-resolved capabilities also alloed us to directly probe the spin-polarization of excited states far out-of-equilibrium,” says dr. oliver j. clark.

the data show a “kink” structure in transiently occupied energy-momentum dispersion of surface states, which can be interpreted as an increase in effective electron mass. the authors were able to show that this mass enhment plays a decisive role in determining the complex interplay inna dynamical behaviors of electrons from the bulk na surface, also dep'on their spin, folloing the ultrafast optical excitation.

“our research reveals which primordial properties of this class of materials are the key to systematically control the relevant time scales in which lossless spin-polarised currents ‘d be generated and manipul8d,” explains sánchez-barriga. these are primordial steps onna way to spintronic devices which based on topological materials possess advanced functionalities for ultrafast information processing.

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original content at: www.scidaily.com…
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